This application claims priority to U.S. Provisional Application No. 60/809,901, filed May 31, 2006, which is hereby fully incorporated by reference.
In recent years, one important area of research and development in wireless communications has been multiple-input multiple-output (MIMO) development. MIMO allows for multiple antennas to broadcast messages simultaneously, resulting in significant increases in throughput and range at a similar bandwidth and power expenditure as single-input single-output systems (SISO).
One concern with wireless communications is spatial diversity. Spatial diversity results when a message is obstructed by some external phenomena. For example, a mountain may be blocking a wireless transmission. In general, MIMO technology increases the spatial diversity of a wireless communication system by including multiple antennas. However, this spatial diversity comes at a price. MIMO communication systems generally function by sending out non-constant envelope signals. These signals require linear amplification which utilizes less efficient amplifiers that consume more power, generate more heat and are more expensive than other amplifier counterparts used in constant envelope signaling.
Additionally, by using non-constant envelope signaling, standard MIMO techniques do not address frequency diversity power efficiently. Frequency diversity results when a single message is broadcast over several frequencies simultaneously. By utilizing frequency diversity, the chances of a receiver receiving a non-distorted signal are increased.
Therefore, there is a need for a MIMO transmission approach that avoids low efficiency, below saturation amplification while providing frequency diversity via OFDM. The present invention fulfills this need among others.